Advertisement

WATER A PRECIOUS RESOURCE 7th CLASS

INTRODUCTION

  We all depend on the same vital substance water, diverse by its nature, it is solid, vapour and liquid. It is in the air, on the earth surface and within the ground ever-changing and giving shape to a dramatic range of natural ecosystem.
  For the earth’s inhabitants, diversity of the resource also means great disparities in well being and development. As we degrade the quality of our water and modify the natural ecosystems on which people and life depend, we also threaten our      own survival.

AVAILABILITY OF WATER

Water is the most widely occurring substance on this planet. Water has shaped the earth’s evolution and continues to fasion its programmes. This is the water preCipitated from the atmosphere on to land, where it may be stored in liquid or solid form, and can move laterally and vertically and between one phase and another phase by evaporation, condensation, freezing and thawing on the land surface. This water can travel at widely differing velocities usually by predictable pathway's which can slowly change with time. We are aware that about 71 % of the earth's surface is covered with water. Almost all the water on the earth is contained in the seas and oceans, rivers, lakes , ice caps, as groundwater and in the atmosphere. However, most of this water is not fit for human consumption.

CMPOSITION OF WATERO

Water is a compound. Its constituent elements are hydrogen and oxygen. Water is a stable compound, but can be broken into hydrogen and oxygen when electric current is passed through it. Its chemical formula is H2O.

PHYSICAL PROPERTIES OF WATER


    The properties of water are different from those of oxygen and hydrogen. For example, water extinguishes fire, but oxygen supports combustion and hydrogen burns with pop sound.
1.    Pure water is a colourless, odourless, tasteless, transparent liquid.
2.    Water exists in all the three stales, solid (as ice), liquid (as water) and gas (as water vapour).
3.    Pure water boils at 100°C.
4.    Pure water freezes at 0°C.

FORMS OF WATER

When water circulates through the water cycle it can be found in all the three forms i.e., solid, liquid and gas· at any given time somewhere on the earth. The solid form, snow and ice, is present as ice caps at he poles of the earth, snow covered mountains and glaciers. Liquid water is present in oceans, lakes, rivers and even underground. The gaseous form is the water vapour present in the air around us, The continuous cycling of water among its three forms keeps the total amount of water on the earth constant.

WATER CYCLE

  The supply of water in nature does not run out. This is because water is continuously recycled in the water cycle.
1.     Heat from the sun causes the water on the earth's surface to evaporate. The vapour rises, cools and condenses to form tiny water droplets. These droplets form clouds.
2.    The clouds get carried along by air currents. They cool and the droplets join to form larger drops. These fall as mist.
3.     If the temperature in the region is very low, these water droplets fall as hail, sleet or snow,
4.     Some of the rain water flows along the ground as streams. Some soaks through the ground and then reappears as springs, Streams and springs join to form rivers. Rivers flow back into the sea. Thus the water cycle is complete.


IMPORTANT SOURCE OF WATER

    Ground water is an important source of water. If we dig a hole in the ground near a water

...
we may find that the soil is moist. The moisture in the soil indicates the presence of water underground. If we dig deeper and deeper, we would reach a level where all the space between particles of soil and gaps between rocks are filled with water. The upper 'limit of this layer is called the water table. The water table varies from place to place, and it may even change at a given place. The water table may be at a depth of less than a metre or may be several metres below the ground. The water found below the water table is called groundwater. What is the source of this groundwater? The rainwater and water from other sources such as rivers and ponds seeps through the soil and fills the empty spaces and cracks deep below the ground. The process of seeping of water into the ground is called infiltration. The groundwater thus gets recharged by this process. At some places the groundwater is stored between layers of hard rocks below the water table. This is a known as a aquifer. Water in the aquifers can be usually pumped out with the help of tube wells or handpumps, We have at many places in India an age old practice of water storage and water recharge like the bawris. Bawris was the traditional way of collecting water.


DEPLETION OF WATER TABLE

   Increase in population, industrial and agricultural activities are some common factors affecting water table. Scanty rainfall is another factor that may deplete the water table.
(a)     Increasing population : Increasing population creates demand for construction of houses, shops. offices, roads and pavements. This decreases the open areas like parks and playgrounds, This, in turn, decreases the seepage of rainwater into the ground. Moreover a huge amount of water is required for construction work. Often groundwater is used for this purpose. So. on one hand we are consuming more groundwater, and on the other we are allowing lesser water to seep into the ground.
(b)     Increasing Industries: Water is used by all the industries. Almost everything that we use needs water somewhere in its production process. The number of industries is increasing continuously. Water used by most of the industries is drawn from the ground.
(c)    Agricultural Activities: A majority of farmers in India depend upon rains for irrigating their crops. Irrigation systems such as canals are there only in a few places. Even these systems may suffer from lack of water due to erratic rainfall. Therefore, farmers have to use groundwater for irrigaiton. Population pressure on agriculture forces increasing use of groundwater day by day. This results in depletion of water table.

WATER MANAGEMENT

  We have seen that most of the water that we get as rainfall just flows away. This is a waste of precious natural resource. The rainwater can be used to recharge the groundwater. This is referred to as water harvesting or rainwater harvesting. We have at many places in India an age old practice of water storage and water recharge like the bawris. Sawri was the traditional way of collecting water. With time the bawris fell into disuse and garbage started piling these reservoirs. However, because ofthe acute water shortage, people in these areas have had to rethink. The bawris are being revived. Today the situation is that inspite of scanty rains these places are managing their water needs well. A farmer using water in the field can also use water economically. May be you have heard of drip irrigation. Drip irrigation is a technique of watering plants by making use of narrow tubings which deliver water directly at the base of the plant.

EFFECT OF WATER SCARCITY ON PLANTS

    Plants need water to get nutrients from the soil 10 prepare their food. Just Imagine the consequences if water is not available to plants. The green character of the planet shall be lost. This may mean the end of all life, for a world without plants shall mean no food, no oxygen. not enough rain, and innumerable other problems .

WASTEWATER

    All materials that do not have immediate utili y and are usually disposed off are called waste. Wastewater is any water that has been adversely affected in quality by anthropogenic (produced by human beings) Influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry andior agriculture.

CLEANING OF WASTEWATER

    Cleaning of wastewater is a process of removing poflutants before it enters a water bGdy or is revised. This process is known as "sewage treatment". In a home or a public building generally one set of pipes brings clean water and another set of pipes takes away wastewater. There is an underground network of big and small pipes, called sewers, forming the sewerage. It is like a transport system that carries sewage from the point of being produced to the point of disposal. i.e. treatment plant. Manholes are located at every 50m to 60 m in the sewage, at the junction of two or more sewers and at points where there is a change in direction .


    Waster water treatment plant (WWTP) 

    Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminate the wastewater.
1.    Waste water is passed through bar screens where large objects like rags, sticks, cans, plastic packets, napkins are removed.
2.    Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to,settle down.
3.    The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water.
    The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.
4.     Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water. 
    After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top. The activated sludge is about 97% water. The water is removed by sand drying beds or machines. Dried sludge is used as manure, returning organiC matter and nutrients to the soil. The treated water has a very low level of organic material and suspended matter. It is discharged into a sea, a river or into the ground. Nature cleans it up further. Sometimes it may be necessary to disinfect water with chemicals like chlorine and ozone before releasing it into the distribution system .

BETTER HOUSE KEEPING PRACTICES

    Waste generation is a natural part of human activity. But we can limit the type of waste and quantity of waste produced.
•    Cooking oil and fats should not be thrown down the drain. They can harden and block the pipes. In an open drain the fats clog the soil pores reducing its effectiveness in filtering water. Throw oil and fats in the dustbin.
•    Chemicals like paints, solvents, insecticides, motor oil, medicines may kill microbes that help purify water. So do not throw them down the drain. Used tealeaves, solid food remains, soft toys, cotton, sanitary towels, etc. should also be thrown in the dustbin. These wastes choke the drains. They do not allow free flow of oxygen. This hampers the degradation process.    

IMPORTANT POINTS

1.    The world water day is celebrated on 22 march every year.
2.    The period 2005-2015 was proclaimed as the international decade for action on "water for life" by the general assembly of the united nations.
3.    BOD (Biological Oxygen Demand) : It is a measure of the oxygen utilised by microorganisms during oxidation of organic materials.
4.    COD (Chemical Oxygen Demand) : It is an index of the waste (organic and inorganic) of water which can be oxidised by strong oxidising agents.
5.    Eutrophication: The excessive growth of algae and aquatic plants due to added nutrients is called eutrophication.

EXERCISE I

Q.1    Explain how ground water is recharged?

Q.2    You have been asked to maintain a garden. How would you minimise the use of water?

Q.3    Write equation for the following reactions.
    (a) action of steam on iron.
    (b) action of cold water on sodium metal.

Q.4    Explain water cycle.

Q.5    List the physical properties of water.

Q.6    What is sewage? Explain why is it harmful to discharge untreated sewage into rivers or seas.

EXERCISE II

Q.1    Water which is absolutely pure and free from any impurity is known as
    (A) boiled water                    (B) mineral water
    (C) distilled water                 (D) None of these


Q.2     Solubility of sugar in water
    (A) decrease with increase in temperature
    (B) increase with increase in temperature
    (C) is not affected by temperature
    (D) None of these


Q.3     Which of these statements is true ?
    (A) Density of ice is more than the density of water.
    (B) Volume of ice is more than the volume of watec
    (C) Temperature of ice is more than the temperature of water
    (D) None of these


Q.4    Pure water is 
    A) an element                           (B) a compound
    (C) a mixture                           (D) None of these


Q.5     Water is called universal solvent because
    (A) it can dissolve all the liquids in the universe
    (B) it dissolve all the gases in the universe
    (C) it dissolve large number of solids, liquids and gases
    (D) None of these


Q.6     What percentage of water is in our body ?
    (A) 30%                                    (B) 70%
    (C) 20%                                   (D) None of these


Q.7     Which of these is the surface water?
    (A) Lakes and rivers               (B) Wells
    (C) Distilied water                  (D) None of these


Q.8     The boiling point of water on plains is 100°C . At hills it will be
    (A) 100°C                               (B) more than 100°C
    (C) less than 100°C                (D) None of these


Q.9     The purest form of natural water is !
    (A) rain water                        (B) ground water
    (C) surface water                   (D) None of these


Q.10     Solubility of gases in water.
    (A) increase with increase in temperature
    (B) decreases with decrease in temperature
    (C) decrease with increase in temperature
    (D) None of these


Q.11     Water at room temperature is 
    (A) solid                               (B) liquid
    (C) gas                                 (D) None of these


Q.12     Water has maximum density at 
    (A) 0°C                               (B) 10°C
    (C) 4°C                              (D) None of these


Q.13     How much of the earth surface is covered with water?
    (A) About 1/3rd                  (B) About 1 14th
    (C) About 3/4th                 (D) None of these


Q.14     The liquids that dissolve in water are called 
    (A) insoluble liquids     
    (B) miscible liquids
    (C) immiscible liquids 
    (D) None of these


Q.15     The ratio of the number of hydrogen atoms and those of oxygen in water is
    (A) 2 : 1                                   (B) 1 : 2
    (C) 2 : 2                                   (D) None of these


Q.16    How much water is available for our consumption?
    (A) 0.01 %                              (B) 1%
    (C) 10%                                  (D) None of these


Q.17    Which of these has the lowest density?
    (A) Ice                                    (B) Water at 1°C
    (C) Water at 4°C                    (D) None of these


Q.18    The continuous circulation of water in nature is:
    (A) hydrological cycle 
    (B) nitrogen cycle
    (C) ground water     
    (D) None of these


Q.19    Water is used as coolant in engines because:
    (A) it makes us feel cold
    (B) it freezes easily
    (C) it has a high specific heat
    (D) none of these


Q.20     We get common salt from 
    A) ground water                       (B) rain water
    (C) sea water                           (D) None of these


Q.21     Water fit for drinking is
    (A) saline water                      (B) soft water
    (C) potable water                   (D) None of these


Q.22     The method of watering the roots of plants directly is
    (A) surface water harvesting 
    (B) drip irrigation
    (C) water table 
    (D) None of these


Q.23     Water harvesting is done to
    (A) store water underground
    (B) store water in fields
    (C) distribute water in fields
    (D) None of these


Q.24    Water that lathers easily with soap is
    (A) hard water                      (B) soft water
    (C) saline water                   (D) None of these


Q.25    The process of removing salt from sea water is called 
    (A) chlorination     
    (B) desalination
    (C) sedimentation     
    (D) None of these


Q.26     Discharge of wastewater generated from manufacturing plants/industries is 
    (A) sewage     
    (B) mining
    (C) industrial effluent 
    (D) None of these


Q.27     Primary treatment is also known as 
    (A) chemical process
    (B) mechanical process
    (C) biological process
    (D) None of these


Q.28     Light floatable water that r,ises to the top during wastewater treatments is 
    (A) sludge     
    (B) scum
    (C) 80th (A) and (B)     
    (D) None of these


Q.29     In sewage, nitrates and phosphates are 
    (A) nutrients    
    (B) inorganic impurities
    (C) organic Impurities
    (D) None of these


Q.30    The diseases caused by bacteria in polluted water is
    (A) Cholera     
    (B) Typhoid

   (C) Both (A) and (B) 
   (D) None of these

 

ANSWER KEY

1.    C                     2.    A                  3.    B                 4.    B

5.     C                    6.     B                 7.     A                8.     C

9.     A                   10.     C                11.     B              12.     C

13.     C                 14.     B                15.     A             16.     B

17.     A                 18.     A                19.    C              20.    C

21.     C                 22.     B                23.     A             24.    B 

25.    B                  26.     C                27.     B             28.     A  

29.    B                  30.    C

EXERCISE I

SECTION-A
•    Fill in the blanks
1.    Water occurs in nature two forms. These are _________________ and _________________.
2.    Only _________________percent of total water resources of the world are usuable.
3.    _________________ can be done to increase the level of water table.
4.    Mineral water is often called _________________
5.    Groundwater is drawn from _________________, ______________ and _________________
6.    Use of _________________and _________________ for irrigation reduces wastage of water.
7.    Ocean water is _________________to taste.
8.    _____________percent of earth surface is covered by oceans.
9.    About _______% of water is present in oceans and seas.
10.    The water bearing layer of the earth is _________________.

SECTION-B
•    True or False

1.    Water occurs in the solid form in glaciers and ice-caps.    
2.    Deforestation increases the level of groundwater.    
3.    Rainwater harvesting is a method of raising water table    
4.    Farmers rely on ground water for irrigating the crops when there is no rain.    
5.    Infiltration is the process of seeping water into the ground    
6.    22 March is celebrated as World Water day.        
7.    Groundwater is usually pure and can be used for drinking    
8.    Water on earth has been maintained by water cycle.    
9.    Increasing population is the cause of depletion of water table.    
10.    Water shortage is a problem faced only by people living in rural areas.    

EXERCISE II


SECTION-A
•    Very Short Questions                             (1 mark each)

1.    Level where space between particles of soil and gaps between rocks are filled with water.
2.    Increase of CO2 in the atmosphere known as
3.    Layer of water below the water table.
4.    Flow of water below the water table
5.    What is fresh water?
6.    What is Mineral water?
7.    What is conservation of water?

SECTION-B
•    Short Questions                                 (2 marks each)

1.    Write two conservation step of water Management?
2.    What is effect of water scarcity on plants.
3.    How industries are causing depletion of water table?
4.    What is the traditional method of water recharge?
5.    What are different forms of water in Nature?

SECTION-C
•    Long Questions                                 (3 marks each)

1.    How is water supplied in the cities?
2.    How are open drains hazardous.
3.    Why should we not throw cooking oil in drains.
4.    What role will you play to minimise wastage of water?
5.    Why water is considered as Universal solvent

SECTION-D
•    Long Questions                                 (4 marks each)

1.    What is Rainwater harvesting? How does it help to solve the water problem?
2.    Mention factors responsible for the depletion of water table
3.    Describe some of the methods by which you can conserve water?
4.    What are sources of ground water? How can it be drawn for use?
5.    Draw flow chart of water Cycle.

EXERCISE III

SECTION-A
•    Multiple Choice Questions (NTSE competition Based)

1.    Which of the following is the purest form of water?
    (A)    Ocean water            (B)    Rain water
    (C) River water                (D)    Ground water
2.    Which of the following is not responsible for water shortage?
    (A) Increasing population                             (B)    Rainwater harvesting
    (C)    More number of industries                  (D)    Mismanagement of water resources
3.    In household which water is used
    (A) Ground water                      (B)    Surface water
    (C)    Ocean water                     (D)    Both (A) and (B)
4.    Which of the following activities uses maximum water?
    (A)    Industry                           (B)    Domestic needs    
    (C) Agriculture                         (D)    Construction of buildings and roads
5.    Which of the following water is not usuable?
    (A)Ocean water                       (B)    Surface water    
    (C)    Ground water                (D)    Construction of buildings and roads
6.    The total water
    (A)    In the lakes and rivers of the world remain constant
    (B)    Under the ground remains constant
    (C)    In the seas and oceans of the world remains constant
    (D)    None of these
7.    Water is
    (A)    Only in solid form             (B)    Only in liquid form
    (C)    Only in gaseous form        (D)    in all three forms
8.    In filtration is
    (A)    Process of seeping of water into ground
    (B) Filtration of water
    (C)    Water stored between rocks
    (D)    All of these
9.    Which of the following is a not a form of water formed by condensation?
    (A)    Dew        (B)    Fog         (C)   Mist        (D)    Spring
10.    What is the name given to the energy made from water?
    (A)    Hydro electricity                    (B)    Thermal electricity
    (C)    Geothermal electricity           (D)    Hydrological electricity
11.    What is water made up of
    (A)    Nitrogen                               (B)    Carbon and Oxygen    
    (C)    Carbon and Hydrogen         (D) Hydrogen and Oxygen
12.    Water is used over and over again in a never ending cycle. What is this cycle called
    (A)    Water ring                         (B)    Hydrological cycle
    (C)    Water Recycling loop       (D)    Water Cycle
13.    Drinking water sources can be contaminated by
    (A)    Naturally occuring materials      (B)    Runoff from farm fields, parking lots and streets
    (C) Both (A) and (B)                           (D) None of these
14.    Water that is safe to drink?
    (A) Potable                (B)    Pilated               (C)    Placoid                (D)    None
15.    Most of the pure drinkable water of the earth is in the form of
    (A) Ice bergs                                  (B)    Vapour and clouds    
    (C) Spring and River water           (D)    Water in the Oceans
16.    Upper limit of the ground water is known as
    (A)    Water ring             (B)    Water loop              (C)    Water table                (D)    All of the above
17.    Depletion of water table is taking place due to
    (A)    Increasing population                (B)    Increasing industries
    (C)    Agricultural activities                (D)    All of the above
18.    Activities followed to reduce the scarcity of water
    (A)    Rain water harvesting               (B)    Bawris (Stroring water)
    (C)    Drip irrigation                           (D)    All of the above
19.    Water pollution is caused by
    (A)    Fertilizers and pesticides          (B) Industrial waste 
    (C) Agricultural farms                       (D) All
20.    Groundwater is drawn from
    (A)    Tubewells              (B)    Hand pumps              (C)    Wells                 (D)    All of the above

SECTION-B 

•    One Word
1.    How much amount of water was recommended by the United Nations for drinking, washing cooking and maintaining proper hygiene per person per day?
2.    What is infiltration?
3.    What is aquifier?
4.    How much earth’s surface is covered with water?
5.    If in a locality a number of tube wells are dug, give one long term impact on the water table.
6.    What are Bawris?
7.    Name any two factors which are causing water table depletion.
8.    By which process ground water gets recharged.
9.    Write two ways through which we adopt to minimise the wastage of water.
10.    Give one difference between groundwater and rain water.

ANSWERS

EXERCISE-I

SECTION-A
1.    Surface, Underground                       2.    3%
3.    Rainwater Harvesting                       4.    Spring water
5.    Tubewells, Handpumps, wells         6.    Sprinkless, Drip method
7.    Salty                                                 8.    71%
9.    97%                                                 10.    Water table                

SECTION-B
    1. True        2. False    3. True        4. True        5. True
    6. True        7. True        8. True        9. True        10. False

EXERCISE-III

Section-A.
    1.    (D)          2.    (B)         3.    (A)       4.    (C)        5.    (A)
    6.    (B)          7.    (D)        8.    (A)       9.    (D)        10.    (A)
   11.    (D)        12.    (D)       13.    (C)    14.    (A)       15.    (A)
   16.    (C)        17.    (D)       18.    (D)    19.    (D)       20.    (D)